The invention relates to the field of self-propelled wheelchairs and comprises a highly efficient, battery powered, hydraulically driven wheelchair which requires substantially less battery power for propulsion than that needed for the all electric drive wheelchairs currently known to the art.
A self-propelled wheelchair can be a crucial possession for the permanently disabled or for one recovering from accident or illness and may sometimes be the only viable means for providing the mobility needed for normal daily activities. In recent years, wheelchair development has improved dramatically with the once manually actuated wheelchair now being superseded by chairs having electric drive motors connected to the wheels to allow patients who lack necessary arm strength or coordination to enjoy new mobility. While these known self-propelled chairs represent a significant improvement, their all electric drive systems encounter serious problems when confronted with prolonged slow speed operation or continual stopping and starting while operating on battery power. Typically, the electric drive wheelchairs are used in indoor corridors or public walkways among pedestrians, and consequently they cannot be operated at greater than walking speeds. Because the chairs are frequently operated indoors or in environments where low noise is essential, only electric storage batteries are practical for energizing such chairs. It seems probable that battery power will continue to be the principal means for energizing the self-propelled wheelchairs and that such power must be used more effectively. While the use of an internal combustion engine has been considered, it is generally not practical because of the presence of exhaust fumes, higher noise generation, and the potential problems of starting or stalling, which cannot be easily handled by a wheelchair operator. The problems of low speed wheelchair operation and the necessity of using a battery power source have placed challenging constraints on wheelchair design, and until the present invention, these problems have defied solution.
Current state of the art chairs use twin electric DC drive motors, with each motor being coupled to a drive wheel of the chair. A heavy storage battery is carried with the chair and is used to energize these motors. Each chair carries as large a storage battery as possible so as to increase the chair's cruising range and to require less frequent recharging of batteries.
Because self-propelled wheelchairs operate at such low speeds, the electric drive motors seldom operate at the optimum speeds for which they were designed, and they tend to overheat and are prone to burnout. These problems have resulted in the chairs being provided with large heat sinks and special motor controllers so as to dissipate the heat buildup and protect the motors from overload and burnout. These drive motors and heat dissipation systems are generally expensive, and repair or replacement of burned out or damaged components can be high cost items. Even with the best available heat dissipation systems, the motors always operate on the hot side and are prone to early failure. In many instances, the entire wheelchair must be brought to a service center for repair when any part of the drive system fails. It will be appreciated that when the electric motors operate at low speed, heavier than usual currents are drawn from the battery to start the D.C. motors and to sustain the low speed operation, resulting in reduced battery life. Still another highly challenging problem is that wheelchair operation has traditionally been limited to level surfaces and those surfaces having grades less than 7%. This can severely limit the areas and places accessible to the handicapped, and it is desirable to provide wheelchairs which can successfully traverse higher grades. It is common for electrically driven wheelchairs to be required to stop at 30 and 40 foot intervals while traversing a 7% grade simply to cool the motors. It is seldom convenient to stop the chair on a grade to cool the motors, and such difficulties, as a practical matter, discourage the use of the chair on even moderate grades. The higher levels of battery power consumption required by slow speed, uphill grade climbing further discourage the use of the presently available, all electric drive chairs on such grades.
It is desirable to provide an improved wheelchair drive system which can climb steeper grades, is not subject to overheating and needs less battery power than the currently used, all electric drive system. The present invention solves these problems and comprises a hydraulically driven wheelchair which increases battery life and significantly increases grade climbing ability.